History of the Company – How & Why We Got Into Post-Tensioning
Our structural consulting engineering firm, Weatherford & Associates, inc., has been in business since 1990. We have provided structural designs for numerous types of projects including commercial, industrial, educational facilities, military facilities, municipal structures, bridges, as well as residences. We have also provided structural engineering consulting services for foundation repairs.
In central Alabama, we have considerable areas overlaid with expansive clay soils. These plastic clays undergo extreme volume change due to the soil moisture variation. During wet periods, they increase in volume (swell) and during dry periods, they decrease in volume (shrink). The cyclic coil volume changes make shallow bearing foundations and slab on ground structures susceptible to horizontal and vertical movements, which often lead to cracking in the exterior and interior walls and ceiling finishes.
Although post-tension slab on ground construction has been used since the 1960s and was approved for residential use by the V.A. and F.H.A. in 1967, Weatherford and Associates did not get involved with designing or recommending such structures until approximately 3 years ago. Until the 1990s, the designs were basically done by “rules of thumb” and correlated only with the plasticity index (PI) of the soil – only one parameter. In the 1980s (and continuing today), the Post-Tension Institute (PTI) became the governing identity for post-tension slab on ground design. PTI has worked to develop methods of predicting soil volume changes based upon not only the soil PI, but climate, drainage, vegetative cover, soil confinement, and other factors. Through these efforts, we now have a method to predict and quantify the soil activity, and we can now perform a true rational design using calculated shears and moments. The current International Building Code (IBC) now requires that all slab on ground foundations in expansive soils be designed using a rational method.
In 2004, a local homebuilder asked if we would provide post-tension slab on ground designs for a group of tract homes that they were planning in an expansive clay soil area. Because there were no locally available qualified tendon fabricators or installers, we were hesitant to provide designs that might not be properly constructed. This led us to create Post-Tension Technologies, L.L.C., which fabricates, installs, and stresses (jacks) the tendons. Post-Tension Technologies is a member of the Post-Tension Institute (PTI) and we have PTI certified installers and PTI certified inspectors.